WASHINGTON – Federal investigators have tentatively set Sept. 9 for the final report on the cause of a fatal UPS plane crash in Alabama a year ago, while the freight carrier's pilots' union used the anniversary to reiterate its call for a change in rest rules for cargo flight crews.

UPS countered that the union "has chosen to play politics," insisting there is no need to change the rest rules for its crews.

The National Transportation Safety Board has not publicly announced the Sept. 9 hearing, but an aviation industry source confirmed the date.

The pilot and co-pilot of the UPS flight complained of fatigue before taking off from Louisville, according to an NTSB transcript of the cockpit conversation before the accident.

Board investigators did not directly connect the crew's fatigue and the instrument errors at the February hearing, but they were the focus of much of the daylong proceeding.

It is likely board members will determine a probable cause for the tragedy at its final meeting on the crash.

In February, then-Chairwoman Deborah Hersman said she hoped the NTSB would conclude the investigation and determine the probable cause before the crash anniversary. But she left the board in late April to become president and CEO of the National Safety Council.

UPS Capt. Cerea Beal, 58, of Matthews, N.C., and First Officer Shanda Carney Fanning, 37, of Lynchburg, Tenn., were killed in the early morning of Aug. 14, 2013, as their Airbus A300-600 clipped trees and hit a hill less than a mile from the end of a 7,000-foot runway at Birmingham-Shuttlesworth International Airport.

As Beal and Fanning prepared their jet for takeoff from Louisville a little more than an hour before the accident, they discussed how tired they were and agreed that more stringent rest rules that were soon to be required for pilots of commercial passenger flights should apply to them as well.

"Yeah, we need that too," Beal said, according to the transcript of the cockpit conversation released by the NTSB. "It should be one level of safety for everybody."

UPS spokesman Mike Mangeot said in February that Beal had been off for eight days before beginning his last trip, and Fanning had flown only two of the previous 10 days.

The cargo airline's officials told the NTSB that company policies emphasize the need for proper crew rest, adding that UPS has a system under which pilots and co-pilots are given a shared responsibility for ensuring they are not tired when they report for duty.

However, the union representing the UPS pilots has insisted there should not be any difference between rest rules for passenger airline pilots and cargo pilots.

Capt. Robert Travis, president of the Independent Pilots Association, reinforced that message in a statement ahead of the anniversary of the crash.

"What we didn't know then, but suspected, was the role fatigue played in this accident," Travis said. "Once the cockpit voice recorder transcripts were released there was no doubt. Cerea and Shanda told us on the CVR that they were fatigued and wanted one level of safety in commercial aviation."

Jim Hall, a former NTSB chairman, joined Travis in criticizing the so-called "carve out" for cargo crews in the fatigue rules, saying it "puts our nation's entire aviation system at risk."

"A tired pilot is a tired pilot, regardless of the plane he or she may be flying," Hall said.

But Mangeot responded that "UPS places the highest emphasis on safety."

"It is unfortunate that the leadership of our pilots' union has chosen to play politics with the memory of our co-workers," he said in a statement. "Doubly unfortunate is that IPA leadership is distorting the facts of the accident investigation to advance its agenda on crew scheduling."

The two crew members who were killed were following schedules that would have complied with the new rest rules for commercial airline pilots, Mangeot said.

If the NTSB determines that fatigue was a factor in the crash, it could recommend changes to federal rest rules or even eliminate any exception for cargo pilots.

But the board does not have the power to enact such a recommendation. That would be up to the Federal Aviation Administration.

Reporter James R. Carroll can be reached at (703) 854-8945. Follow him on Twitter @JRCarrollCJ.